per the current specification, double spending is not possible on the same block chain, and neither is spending bitcoins without a valid signature. How does one acquire bitcoins? The Bitcoin technology - the protocol and the cryptography - has a strong security track record, and the Bitcoin network is probably the biggest distributed computing project in the world. The Bitcoin protocol is designed in such a way that new bitcoins are created at a fixed rate.
Bitcoin faq deutsch
From a user perspective, Bitcoin is pretty much like cash for the Internet. Users are in full control of their payments and cannot receive unapproved charges such as with credit card fraud. Bitcoin can be used to pay online and in physical stores just like any other form of money. Long synchronization time is only required with full node clients like Bitcoin Core.
No central authority or developer has any power to control or manipulate the system to increase their profits. There is a wide variety of legislation in many different jurisdictions which could cause income, sales, payroll, capital gains, or some other form of tax liability to arise with Bitcoin. Some concerns have been raised that private transactions could be used for illegal purposes with Bitcoin. For some Bitcoin clients to calculate the spendable balance of your Bitcoin wallet and make new transactions, it needs to be aware of all previous transactions. As a global currency you can send bitcoin to anyone, anywhere in the world without worrying about cross border remittance fees.